The purpose of this project is to determine the incidence and etiology of post-transfusion hepatitis in newborn babies. Post-transfusion hepatitis is still a common problem in adults, but at present most cases are of unknown etiology (so-called non-A non-B hepatitis). The hepatitis B virus now causes very few cases among adults and the other known hepatitis agents (hepatitis A virus, cytomegalovirus and Epstein-Barr virus) have not been implicated etiologically. No systematic studies of post-transfusion hepatitis have been conducted in children or newborn babies and both the incidence and etiology of this complication of blood transfusion may be different in the younger age groups than in adults. During the 4 years of the study, 200 transfused newborns and 200 non-transfused control babies will be followed with monthly blood samples for 6 months after transfusion. These samples will routinely be tested for alanine aminotrasferase (ALT) level as the screening technique for hepatitis. Sera wil also be tested for evidence of infection with the known hepatitis viruses and will be stored for future testing of non-A non-B agents when they are identified. Our findings in babies will be compared with those from a similar study conducted in parallel among adults from New York City (part of the national Transfusion Transmitted Viruses study).